Abstract/Summary

Crop rotation, cover crops introduction and no tillage adoption have improved tropical agriculture sustainability through improvements on soil conservation and water use efficiency. Soil fertility and topsoil phosphorus (P) accumulation is also altered by management, affecting P dynamics and its use for subsequent cash crops. Changes in soil P fractions promoted by no-tillage (NT) and conventional tillage (CT) in soybean/cotton crop systems with different cover crop rotations (fallow, maize as second crop, brachiaria and millet) were investigated in two long-term trials in Brazilian Oxisols (Ox-1 and Ox-2), and compared to soils under native Cerrado vegetation. Hedley’s P fractionation was performed in soil samples taken from 0 to 5, 5 to 10 and 10 to 20 cm depth layers and P fractions grouped by their predicted lability. Long-term cultivation generated large amounts of legacy P in the soil (184−341 mg kg−1) but only a small portion remained in labile fractions (11–16 %), with a slight increase in non-labile P (<5 %) and organic P (10–20 %) concentrations under NT when compared to CT. Although the soil P remained mostly in less available fractions, the legacy P obtained by the difference between the soil P data from the agricultural land and the native area provided a useful approach for P accumulation estimative over the time, very close to the predicted P inputs/outputs accounting. Brachiaria recycled more P than other cover crops, increasing the labile P (5–20 %) and all the organic P fractions (10–25 %) over the time.